I. Field
The present invention relates to an oilfield tool and more particularly, to an autonomous magnetic sleeve for a riser which is constructed and arranged to be independently lowered and seated above a subsea tree to capture ferromagnetic materials in the drilling fluid flowing into the riser.
II. Background
Various types of junk baskets have been devised for collecting debris from a wellbore during a cleaning operation. The junk basket has a basket dimensioned to collect debris flowing around and external to the basket. The top end of the junk basket is open and relies on free falling debris in the upward-flowing drilling fluid to fall into the opening of the junk basket where it remains until the junk basket is removed. However, the force of the upward-flowing drilling fluid carrying the debris impedes the collection of the debris by the junk basket.
Thus, some junk baskets are not able to collect a substantial portion of the debris in the wellbore, particularly when fluid circulates through the junk basket and upward through an annulus in the well as the basket is retrieved to the surface. Other junk baskets are complicated and are thus relatively expensive.
FIG. 1 illustrates a conventional junk basket 1 having a central mandrel 2 and a basket 4. The annulus between the wellbore 3 and the basket 4 narrows. Thus, the upward-flowing fluid, denoted by ARROW A, has a first speed. The fluid, denoted by ARROW B, has a second speed faster than the first speed as a result of the narrower annulus. The fluid, denoted by ARROW C, continues upward toward the top of the wellbore 3 and is generally slower than the fluid, denoted by ARROW B. However, as the fluid, denoted by ARROW B, passes the upper end of the basket 4, a portion of the fluid automatically travels, in the direction of ARROW E, toward the central mandrel 2 as the annulus is abruptly enlarged. This portion of the fluid flowing in the direction denoted by ARROW E forms small eddy currents created directly over the opening in the basket 4. However, simultaneously, fluid flowing upward, in the direction of ARROW C, recaptures or carries away the debris. Thus, the deposit of debris in the basket 4 is impeded.
Most junk baskets are positioned at various locations in a work string. However, a significant amount of debris is still carried up to the top of the wellbore. The floating debris must be retrieved and removed from the drilling fluid. However, there is not an efficient or quick means of removing the debris near the top of the wellbore. The slower moving fluid in the riser may not be able to suspend the heavier debris. Thus, the heavier debris floats downward.
There are also a variety of magnetic devices for use in the wellbore. These devices are also installed at various locations in the wellbore. However, a significant amount of ferromagnetic materials remains uncaptured as the fluid enters the riser.
Thus, there is a continuing need for an autonomous magnetic sleeve for use in a riser which is constructed and arranged to be independently lowered and seated above a subsea tree to capture ferromagnetic materials in the drilling fluid flowing into the riser.